Lithium-ion batteries: runaway risk of forming toxic compounds.

Lithium-ion batteries are stabilized by an ultrathin protective film that is 10-50 nanometers thick and coats both electrodes. Here we artificially simulate the 'thermal-runaway' conditions that would arise should this coating be destroyed, which could happen in a battery large enough to overheat beyond 80 degrees C. We find that under these conditions the reaction of the battery electrolyte with the material of the unprotected positive electrode results in the formation of toxic fluoro-organic compounds. Although not a concern for the small units used in today's portable devices, this unexpected chemical hazard should be taken into account as larger and larger lithium-ion batteries are developed, for example for incorporation into electric-powered vehicles.